A microbolometer is a type of bolometer used as a detector in a thermal camera. Infrared radiation strikes the detector material, heating it, and thus changing its electrical resistance. This resistance change is measured and processed into temperatures which can be used to create an image. Unlike other types of infrared detecting equipment, microbolometers do not require cooling.
Microbolometers can be passive or active devices. For example, a passive microbolometer will have a temperature sensitive resistor. An active microbolometer, on the other hand, will have a temperature sensitive transistor. In either scenario, the microbolometer requires a read-out circuit.